Effects of intracerebral administration of IL-1beta on reactive behaviors of astrocytes and macrophages in the injured brain of newborn rats

Newborn male rats were subjected to a mechanical lesion of the left cerebral hemisphere. Thereafter, a single dose 5 or 500 units (U) of recombinant rat interleukin-1 beta (IL-1 beta) was injected into the lesion cavity. One or 2 days after the injury, the rats were injected with H-3-thymidine to label dividing cells. Brain sections were subjected to GFAP immunocytochemistry or BSI-B4 lectin histochemistry to visualise astrocytes or macrophages, respectively. Autoradiography was used to detect cells proliferating within the region of injury in the immunocytochemically stained brain sections. The strongest mitogenic effect of IL-1 beta on astrocytes (labeling index) was observed on day 1 after injury while a dose-dependent increase in their GFAP-immunoreactivity occurred on day 2. At 500U dose, IL-1 beta significantly reduced infiltration of macrophages on posttraumatic days 1 and 2 but did not influence their proliferation. Thus, effects of IL-1 beta on the occurrence of macrophages were opposite to those on the GFAP-immunoreactivity of astrocytes and their proliferation. It appears to suggest existence of different mechanisms controlling reactive behaviors of the two cell populations.